<style>
    .appContent {
        background-color: salmon;
        font-size: 16px;
        margin: 0px;
        padding: 0px;
    }

    p {
        background-color: tomato;
        font-size: 20px;
    }
</style>
<div class="appContent">
    Hello, First World
</div>
<p>
    Global attributes are attributes common to all HTML elements; they can be used on all elements, though they may have no effect on some elements.
</p>